1. Field of the Invention
The present invention relates to a helical antenna in which radiation elements are provided in helical form on the surface of a cylindrical member composed of a dielectric, and to a method of manufacturing this helical antenna.
2. Description of the Related Art
Helical antennas are used as the antennas for portable terminals in portable telephone systems that employ-non-geostationary satellites. FIG. 1 is a perspective view of an example of this type of helical antenna of the prior art.
Referring to FIG. 1, helical antenna 102 of the prior art is shown that includes element 100, feeder circuit 200, and connection pins 310. Element 100 is formed by winding flexible print circuit board 120 in the form of parallel quadrilaterals around dielectric pipe 110. Flexible print circuit board 120 is secured to dielectric pipe 110 by an adhesive or a double sided tape.
Feeder circuit 200 is formed from circuit board 104 (also referred to as a xe2x80x9cdielectric boardxe2x80x9d) made up from a disk-shaped dielectric having a larger diameter than dielectric pipe 110. Microstrip lines (not shown in the figure) are formed and a chip-type 4-distributor, resistor, and capacitor are mounted on one surface of dielectric board 104, these components having the function of a 4-distributor/combiner circuit. A ground conductor is formed on the other surface of dielectric board 104. Since this type of feeder circuit is well known in the art, and functionally, is not an element that is closely connected to the present invention, a detailed explanation of these components is omitted.
FIG. 2 is a sectional view showing the connection points between element 100 and feeder circuit 200 in helical antenna 102 shown in FIG. 1. In the figure, components identical to those shown in FIG. 1 bear the same reference numerals.
As shown in FIG. 2, a plurality of connection pins 310 are arranged at the edge of element 110. Each of connection pins 310 passes through a through-hole formed in dielectric board 104 of feeder circuit 200. One end of connection pins 310 is soldered to element 100 and the other is soldered to feeder circuit 200.
In the configuration of helical antenna 102 of the prior art, element 100 and dielectric board 104 are connected by inserting connection pins 310 through dielectric board 104, and the outside diameter of feeder circuit 200 is therefore greater than the outside diameter of dielectric pipe 110. This factor is not advantageous for reducing the outside diameter of helical antenna 102.
An antenna that is incorporated into a portable telephone is preferably as compact as possible, and, for example, a helical antenna of the following construction has been proposed to eliminate the above-described drawback.
FIG. 3 is a perspective view showing another example of a helical antenna of the prior art. In the figure, constituent elements identical to those of FIG. 1 bear the same reference numerals.
Helical antenna 106 shown in FIG. 3 includes element 100A, feeder circuit 200A, and connection pins 310. Element 100A is formed by winding flexible print circuit board 120A, which is shaped as a parallel quadrilateral, around dielectric pipe 110A. The outside diameter of feeder circuit 200A is somewhat larger than the outside diameter of element 100. The electrical configuration of feeder circuit 200A is the same as that of feeder circuit 200 shown in FIG. 1.
FIG. 4 is a sectional view showing in detail the connection points between element 100A and feeder circuit 200A in the helical antenna 106 shown in FIG. 3. In the figure, constituent elements that are the same as those shown in FIG. 3 bear the same reference numerals.
The walls of dielectric pipe 110A are thicker on the side of feeder circuit 200A than in other portions of dielectric pipe 110A. and holes for inserting connection pins 310 are formed in this thicker portion of dielectric pipe 110A. Flexible print circuit board 120A is wound around dielectric pipe 110A such that its lower end-bends inwards at the lower end of dielectric pipe 110A. Flexible print circuit board 120A is secured to dielectric pipe 110A by means of an adhesive or a double sided tape.
The upper ends of connection pins 310 are inserted into the above-described holes in dielectric pipe 110A, and the lower ends are inserted into through-holes formed in dielectric board 104 of feeder circuit 200A. Connection pins 310 are then connected to feeder circuit 200A by soldering at these through-holes. The upper ends of connection pins 310, on the other hand, are soldered to the end of flexible print circuit board 120A that is bent inside dielectric pipe 110A.
This helical antenna 106 allows each of connection pins 310 to be provided at points closer to the center of dielectric board 104 than in helical antenna 102 shown in FIG. 1, and the outside diameter of feeder circuit 200A can therefore be made smaller than that of feeder circuit 200 shown in FIG. 1.
Nevertheless, this helical antenna 106 has the drawback that the process of winding flexible print circuit board 120A around dielectric pipe 110A is complicated by the necessity of bending the lower end of flexible print circuit board 120A inside the lower end of dielectric pipe 110A. A further drawback is the increased number of fabrication steps required for forming holes in dielectric pipe 110A for inserting connection pins 310.
It is an object of the present invention to provide a helical antenna that is compact and that can be assembled reliably in a short time, as well as a method of fabricating the helical antenna.
To achieve the above-described objects, the helical antenna according to the present invention comprises a plurality of radiation elements provided in helical form that are spaced at intervals from each other on the outer surface of a cylindrical member that is composed of a dielectric, a circuit board on which is mounted a feeder circuit for supplying high-frequency energy to the radiation elements, and a connector for electrically connecting the radiation elements and the circuit board. The circuit board is arranged below the cylindrical member, and the connector is arranged between the lower end of the cylindrical member and the circuit board. The connector is composed of an insulating material and is provided as a solid unit with a plurality of connection pins that electrically connect the end of each radiation element with the circuit board.
According to a preferable embodiment of the present invention, the connector includes a connector body, and the plurality of connection pins are provided on the connector body. The connector body includes a lower portion that is formed with an outside diameter that is substantially equal to the outside diameter of the cylindrical member and an upper portion that is formed with an outside diameter that allows insertion inside the cylindrical member with substantially no gap. The lower ends of the connection pins protrude downward from the lower surface of the lower portion of the connector body. The upper ends of the connection pins protrude upward from the lower portion of connector body with a gap between the connection pins and the outer surface of the upper portion of the connector body. The connector body is then joined to the cylindrical member by inserting the upper portion of the connector body into the lower end of the cylindrical member and interposing the lower end of the cylindrical member between the outer surface of the upper portion of the connector body and the upper ends of the connection pins. The upper ends of the connection pins are thus electrically connected to the ends of the radiation elements, and moreover, the lower ends of the connection pins are electrically connected to the circuit board.
In the fabrication method of the helical antenna according to the present invention, a cylindrical member, a circuit board, and a connector composed of an insulating material are prepared beforehand. A plurality of helical radiation elements are provided at intervals on the outer surface of the cylindrical member. A feeder circuit for supplying high-frequency energy to the radiation elements is mounted on the circuit board. A plurality of connection pins for electrically connecting the ends of the radiation elements to the circuit board are provided as a solid unit with the connector. Then, the connector is installed on the circuit board and the connection pins are electrically connected to the feeder circuit, and in addition, the connector is attached to the lower end of the cylindrical member and the connection pins are electrically connected to the ends of the radiation elements.
According to a preferable embodiment of the fabrication method of the helical antenna of this invention, the connector includes a connector body composed of an insulating material, and the plurality of connection pins are provided as a solid unit with this connector body. The lower ends of the connection pins protrude downward from the lower surface of the lower portion of the connector body. The upper ends of the connection pins protrude upward from the lower portion of the connector body and form a gap with respect to the outer surface of the upper portion of the connector body. The connector body and cylindrical member are then joined by inserting the upper portion of the connector body into the lower end of the cylindrical member and interposing the lower end of the cylindrical member between the upper ends of the connection pins and the outer surface of the upper portion of the connector body, thereby electrically connecting the upper ends of the connection pins and the ends of the radiation elements, and further, electrically connecting the lower ends of the connection pins to the circuit board.
According to the present invention, radiation elements provided on the outer surface of the cylindrical member are connected by means of a connector to a feeder circuit that is mounted on a circuit board. Accordingly, a connector body provided as a solid unit with connection pins is of a construction that includes a lower portion that is formed with substantially the same outside diameter as the outside diameter of a cylindrical member and an upper portion that is formed with an outside diameter that allows insertion inside the cylindrical member with substantially no gap; the lower ends of the connection pins are configured to protrude from the lower surface of the lower portion of the connector body, and the upper ends of the connection pins are configured to extend upward from the lower portion of the connector body such that a gap is formed between the upper ends of the connection pins and the outer surface of the upper portion of the connector body; whereby the diameter of the circuit board can be made equal to or less than the outside diameter of the cylindrical member. In addition, the diameter of the connector can also be made substantially equal to the diameter of the cylindrical member. As a result, a slimming of the entire helical antenna can be achieved.
When assembling the helical antenna, the cylindrical member and circuit board need only be connected by way of the connector. In particular, a construction in which the connector body includes an upper portion and lower portion as described hereinabove and the upper ends of the connection pins are constructed as described hereinabove enables the radiation elements to be electrically connected to the connection pins by inserting the upper portion of the connector body into the lower end of the cylindrical member and interposing the ends of the radiation elements between the upper ends of the connection pins and the outer surface of the upper portion of the connector body. The ends of the radiation elements and the upper ends of the connection pins may also be soldered together as necessary.
In a case in which the radiation elements are constituted by metal foil patterns formed on a dielectric sheet, the radiation elements can be provided in helical form on the outer surface of the cylindrical member by wrapping the dielectric sheet around a cylindrical member. In this case as well, adopting a construction in which the radiation elements are interposed between the outer surface of the upper portion of the connector body and the upper ends of the connection pins as described above eliminates the need for bending the lower end of the dielectric sheet toward the center of the cylindrical member, as in the prior art, and further, eliminates the need to form holes for inserting connection pins in the end surface of the cylindrical member.
The present invention therefore enables easy, reliable, and speedy assembly of a helical antenna without need for special methods.
In addition, the terms xe2x80x9cupperxe2x80x9d and xe2x80x9clowerxe2x80x9d that are used in the present invention indicate xe2x80x9cupxe2x80x9d and xe2x80x9cdownxe2x80x9d when the helical antenna is in an erect state in which the feeder circuit is positioned below the cylindrical member, and do not necessarily indicate xe2x80x9cupxe2x80x9d or xe2x80x9cdownxe2x80x9d when the helical antenna is in use or when the helical antenna is being assembled.
The above and other objects, features, and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention.